I often see emails being blocked that trigger the double extension filter that a human viewer can instantly recognize as a false positive.
For example: 'itinerary j.doe.pdf' will get filtered.
Since both '.doe' and '.pdf' are safe extensions this shouldn't happen.

I have manually added a few common exceptions already (like .docx.pdf, since people often convert Word documents to PDF) but obviously I can't make exceptions for every possible variation.